An ignition system for an aircraft turbojet engine typically comprises a spark discharge igniter plug located in the engine combustor which is supplied with high voltage oscillatory currents from an exciter circuit. The exciter circuit is located elsehwere on the engine in an environment less hostile than that in the vicinity of the engine combustor. The exciter is connected to the igniter by a length of shielded cable releasably fastened at each end by threaded connectors. For strength and reliability, the threaded parts of the mating connectors at both ends of the cable are formed of steel.
The exciter is enclosed in a hermetically sealed housing, typically formed of aluminum. Creating a reliable hermetic seal between a relatively thin-walled aluminum housing and a steel bodied outlet connector is difficult because of the incompatibility of the dissimilar metals to welding. Heretofore, an output connector having a tubular body formed entirely of steel has been secured to the aluminum exciter housing by a compression-type fitting threaded onto the base end of the connector shell. The connector shell encloses a center conductor pin supported coaxially within the shell by a ceramic insulator. Gas tight seals are formed between the pin and insulator by a fused glass bead and between the insulator and connector shell by a metal skirt or diaphragm bonded along one edge to the outer wall of the insulator and brazed along the other edge to the inner wall of the connector shell at the terminal end thereof. The base portion of the connector shell is hermetically sealed to the exciter housing by a film of solder sweated into place. The solder film forms a seal of weak mechanical strength which is generally inadequate to support the torsional load applied to the connector shell during attachment of the mating connector. Additional mechanical means in the form of pins or keys bridged between the housing and the connector base fitting must therefore be provided to resist torque loading at the connector base and such means are not fully satisfactory to guarantee that the integrity of the solder seal will remain intact.
It is an object of the invention to provide an electrical connector through which an electrical cable may be detachably coupled to circuitry contained within a hermetically sealed housing, the mating parts of the connector being threaded together and formed of high strength materials resistant to wear and damage through over tigthening.
It is another object of the invention to provide a tubular electrical connector having a threaded end portion adapted to receive a mating cable connector and a base portion adapted to be secured in a gas tight, torque resistant relationship to a thin-walled hermetically sealed housing, wherein the connector end portion and base portion are formed of different metals.
It is another object of the invention to provide a tubular connector having a threaded terminal end portion formed of steel and a base portion formed of a metal of a type suitable for welding to aluminum, whereby the connector may be secured to an aluminum housing to form a gas tight, torque resistant seal.
Briefly, the invention comprises an electrical connector having a tubular body or shell, the base portion of which is aluminum and the terminal portion of which is steel. The connector shell is fabricated from a cylindrical blank produced as a transverse punching through a composite laminate of aluminum and steel. The laminate is formed by explosively bonding together a relatively thick plate of steel and a relatively thick plate of aluminum, with the total thickness of the laminate being substantialy equal to the length of the connector shell. The steel portion of the shell is threaded to receive a mating cable connector and the aluminum portion of the shell is sealed by fusion welding into an aperture in a wall of an aluminum housing.